1. Field of the Invention
The invention relates generally to semiconductor wafer processing and, more particularly, to apparatus and methods for eliminating chemical loss during the cleaning of semiconductor wafer surfaces.
2. Description of the Related Art
In electronic device manufacturing operations, expensive proprietary chemical mixtures or blends customarily referred to as “solvents” or “proprietary solvents” are widely used to remove particulate contaminants, post-etch residue, and metal contamination from semiconductor wafer surfaces. Such chemical solvents generally fall into two generic classes: “aqueous-based” solvents and “organic-based” solvents. Aqueous-based solvents are cleaning chemistries which are water-based (i.e. are up to 95% water by weight with the active chemical agents making up the remainder). Organic-based solvents are cleaning chemistries for which water is replaced by a liquid organic chemical, or mixtures thereof, that also contains active chemical agents for cleaning semiconductor wafer surfaces. Because of the expense of obtaining these solvents, they are typically reclaimed after processing and re-used. For example, FIG. 1 illustrates a conventional liquid chemical reclaim system 100. In FIG. 1, a chemical solvent is applied to a surface 104 of a semiconductor wafer 106 from a supply tank 108 via a supply line 112, to create a chemical meniscus 102. The chemical meniscus 102 acts to clean the semiconductor wafer surface 104. Ambient air flow (not shown) is applied to the chemical meniscus 102 to prevent the meniscus 102 from breaking out of a defined footprint and flooding the semiconductor wafer surface 104. As the proximity head 110 moves along the semiconductor wafer surface 104, the chemical solvent of the meniscus 102 operates on the semiconductor wafer surface 104. The chemical solvent is removed from the semiconductor wafer surface 104 using a vacuum mechanism. Specifically, this vacuum mechanism draws the air and chemical solvent from the surface 104 of the semiconductor wafer 106, out of the proximity head 110, and into a vacuum tank 114 via an air-liquid return line 116 coupled to the vacuum tank 114. At the vacuum tank 114, the chemical solvent is separated from the air and the air is pumped out of the vacuum tank 114 via an exhaust 118. Reclaim of the chemical solvent is achieved by recirculation of the chemical solvent from the vacuum tank 114 back to the supply tank 108 via a liquid pump 120.
Evaporation of the chemical solvent in conventional liquid reclaim systems similar to the system 100 illustrated in FIG. 1 is a serious issue. Such evaporation can result in significant changes in cleaning performance due to chemical solvent depletion and/or excessive concentration of chemicals. Chemical solvent depletion occurs because, during standard operation, there is a significant mixing of the chemical meniscus liquid and the ambient air on the way to the vacuum tank 114. Therefore, the air (gas) stream that exists in the vacuum tank 114 through the exhaust 118 is saturated with every component of the volatile chemical solvent. And the chemical solvent included in the saturated gas (air) stream is not reclaimed once the saturated gas (air) stream is out of the vacuum tank 114 and before the saturated gas (air) stream is sent to purification scrubbers.
Excessive concentration of chemicals, on the other hand, commonly results with the use of proprietary solvents. Proprietary solvents contain non-volatile components and, if the proprietary solvent is aqueous-based, evaporation causes the concentration of non-volatile components to increase over time. This increase in the concentration of non-volatile components can adversely affect the cleaning performance of the chemical solvent. Moreover, damage to the semiconductor wafer 106 can result if the concentration of non-volatile components increases too much. Additionally, proprietary solvents are commonly used at elevated temperatures, (e.g. 30 degrees Celsius to 60 degrees Celsius) to get improved cleaning performance. Since evaporation is determined by vapor pressure, which exponentially increases with temperature, chemical loss can dramatically increase, causing a corresponding dramatic decrease in the usable lifetime of a chemical solvent bath.
In view of the foregoing, there is a need for a reclaiming approach that reduces chemical loss due to evaporation and other sources.